A US soldier, center, adjusts parts of a gun during training at the US base of Bagram north of Kabul, Afghanistan, Thursday. President Barack Obama plans to announce a redrawn battle plan for Afghanistan, in a national address Tuesday night.

In making a case for the expansion of the war in Afghanistan Tuesday, President Obama will take up the difficult sales job he has so far largely avoided.

During his term as senator and as a candidate for president, Mr. Obama spoke of Afghanistan in urgent terms, saying during the 2008 campaign: “If another attack on our homeland comes, it will likely come from the same region where 9/11 was planned.”

Since Obama announced his “comprehensive, new strategy for Afghanistan and Pakistan” in March, the Pentagon has steadily undertaken the massive task of reorienting its war-fighting capabilities toward Afghanistan. But with the exception of a few minutes during an August speech to Phoenix veterans, Obama has largely steered clear of any signature defense or explanation of his own policy.

As the president has focused his bully pulpit primarily on healthcare but also on jobs, economic reform, and energy policy in recent months, the Afghan war – and Obama’s handling of it – has lost support among many Democrats in Congress as well as Americans in general.

A USA Today/Gallup poll released last week found that 55 percent of Americans disapprove of how he is handling the war, while 35 percent approve. That marks a reversal from July, when 56 percent of respondents approved, according to USA Today/Gallup.

On Sunday morning talk shows, lawmakers voiced similar doubts. “The president has to outline why Afghanistan is important,” said Sen. Richard Lugar (R) of Indiana on CNN’s “State of the Union.”

In the harsh battlefield assessment that startled the White House and resulted in nine top-level strategy sessions, Gen. Stanley McChrystal, the US commander in Afghanistan, wrote: “Stability in Afghanistan is imperative; if the Afghan government falls to the Taliban – or has insufficient capability to counter transnational terrorists – Afghanistan could again become a base for terrorism…”

After three months of deliberations, it appears that Obama now agrees. Media reports suggest that Obama will approve at least 30,000 more troops for Afghanistan and pressure allies to supply an additional 5,000 to 10,000.

This falls within the range of what McChrystal first requested: some 40,000 more troops.

Now, Obama must take the answers to the questions raised during his strategy summits to the nation on Tuesday – and to Congress shortly after.

Among the issues raised during the meetings that Obama will have to address:

• With Al Qaeda leadership now in Pakistan, why is Afghanistan worth it? Obama is likely to respond to this with McChrystal’s own words: an Al Qaeda hemmed in to a thin sliver of Pakistan is preferable to one that is allowed much freer rein – a probable result of failure in Afghanistan.

Moreover, Afghanistan is a key battleground in the proxy war between India and Pakistan. If Afghanistan grew strong enough to fend off external interference, it could remove one source of tension between two nuclear rivals (and key US allies).

• Is Afghan President Hamid Karzai a reliable partner? The Obama administration still seems wary of Mr. Karzai but appears to be banking on him becoming more proactive against corruption in his government under new US pressure.

Karzai is in a difficult position. He made alliances with corrupt Afghan power brokers in part to survive politically. Essentially enthroned by the international community in 2001, he and his country were largely forgotten for eight years, forcing him to adapt.

With a more robust and engaged US presence behind him, he might be more inclined to heed American anticorruption demands. Reports suggest that new US troops will be phased in over 12 to 18 months, suggesting that Obama might be providing something of a carrot to Karzai: shape up or the next scheduled deployment might not happen.

• Can the US afford to send 30,000 more troops – each at an estimated cost of $1 million a year? “We’re going to have a serious talk about the budget,” said Senator Lugar.

Perhaps even more problematic, however, is the question of how much the US will have to support the Afghan Army and police. Obama’s plan will be based on the idea of handing off security to Afghan soldiers and police as quickly as possible.

But funding forces big enough to protect the country would bankrupt the Afghan government, meaning other countries will have to foot a significant portion of the bill – perhaps well into the future.

“We have not heard how much Afghan troops would cost to us,” Lugar said.